The present invention relates to an improved error correction system for a length or angle measuring device of the type comprising a graduation carrier, which includes a measuring graduation, and a scanning unit, which scans the measuring graduation, wherein the scanning unit and the carrier are adapted to be coupled to two objects which are movable with respect to each other.
A variety of error correction systems for such measuring devices are known to the art. For example, in German DE-AS 25 18 745 there is described a length measuring system in which a linear error correction is brought about by means of a device for elongating or compressing the measuring scale. This device engages the two opposed ends of the scale, and a nonlinear error correction is therefore not possible.
In German DE-AS 27 35 154 there is disclosed a position measuring system in which the measuring scale is deflected at at least one point substantially transversely to the graduation plane in order to bring about desired error corrections. This transverse deflection is brought about by either pressure or traction forces applied to the scale transversely to the graduation plane in correspondence with the desired error correction. Such transverse deflections of a scale bring with them disadvantages when the scanning unit is not guided directly on the graduation plane of the scale. In this case, spacing fluctuations between the scanning unit and the graduation plane of the scale can arise.